Well, I thought I should post an update on the C280 - especially for anyone following this thread later.

Looks like the problem is a cracked insulator on one of the spark plugs. Now, here's the interesting part. This engine has less than 1000 miles on it. It came directly from MB. With the WRONG plugs in it! The plugs were a hotter heat range. Here's the other interesting part. It has a head gasket leak. MB is paying to replace it. But Randy can't figure out why it would leak, unless it had an old gasket in it (as I understand it, the gasket's been re-engineered because of the problems with the old design). I suggested to Randy that MAYBE the engine had been in someone's inventory for a few years...

Anyone have any thoughts on this?

I have a C220 and I had this exact same problem a couple years ago. I also had a damaged engine mount at the time. The car turned into limp mode on me about 5 times over 2 weeks on the freeway and a simple turn off and on corrected the problem....pulling over without any power wuz the scary thing to do cuz ur car starts to slow down in the fast lane....

anyways, i suspected the car needed a tune up...
The shop i took it to replaced the Engine Mounts and did a complete tune up of the car, however during the tune up they noticed that my car's engine wire-harness had fallen apart aswell...so they changed that aswell.

It cost me a few thousand dollars to get everything done that time, mainly due to the price and labour for the harness job. However the problem never re-occured, so I'm guessing u need to look into those 3 things as well.

Miss at 4000
 

The simple answer is have the car checked with a good scanner at HFM and Diag. modules.
Mike